[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20230818142033.1d7685e9@gandalf.local.home>
Date: Fri, 18 Aug 2023 14:20:33 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Francis Laniel <flaniel@...ux.microsoft.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 1/1] tracing/kprobe: Add multi-probe support for
'perf_kprobe' PMU
On Fri, 18 Aug 2023 20:13:43 +0200
Francis Laniel <flaniel@...ux.microsoft.com> wrote:
> Hi.
>
> Le vendredi 18 août 2023, 17:41:41 CEST Steven Rostedt a écrit :
> > On Fri, 18 Aug 2023 21:37:05 +0900
> >
> > Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> > > That's why perf probe uses the offset from '_text'. Normal KASLR will just
> > > moves all symbols. (Finer one will move all symbols randomely)
> > > This should not need to access /proc/kallsyms but vmlinux or SystemMap.
> >
> > We could just pass in: "_text+offset" too.
>
> So, the idea would be to change the existing create_local_trace_kprobe() and
> above functions to indicate the user's offset is to be used against _text and
> not address?
No, not to modify that function, but if you know the offset from _text (via
the vmlinux), you can easily calculate it for that function.
I mentioned having a way to pass in the vmlinux debug info address and
subtract the kaslr_offset from it. But that's actually unnecessary. If you
have the address of the function you want, and the address of _text, both
from the debug info of vmlinux, you can simply pass in "_text+offset", and
then use kallsyms to give you _text, and add the offset to give you the
address for create_local_trace_kprobe().
-- Steve
Powered by blists - more mailing lists